CARLSBAD  After years of shunning proposals for a new gas-fired plant in Carlsbad, San Diego Gas & Electric is taking a fresh look at a possible annex to the 60-year-old Encina Power Station.

Utilities are tearing up and redrawing their road maps to the Southern California power grid in response to the unexpected retirement of the San Onofre Nuclear Generating Station in June. Its two reactors produced 20 percent of San Diego’s electricity, and enough to power 1.4 million homes in Southern California.

SDG&E confirmed that it is in discussions with NRG Energy about its proposed Carlsbad Energy Center, a 558 megawatt addition to the Encina site.

Officials from both companies told Carlsbad City Council members Tuesday night that SDG&E might eventually buy power from the new plant if NRG redesigns it as a “peaker plant,” which would run less often and be less conspicuous than the plant NRG planned to build.

The Carlsbad council, which has long opposed any type of power plant on the site, voted unanimously Tuesday to negotiate a compromise with the two companies over the project. Obtaining new permits for the redesigned plant will take at least 16 months and Carlsbad’s cooperation is key to NRG’s new timeline of starting construction in 2015 and opening the plant in 2017.

City officials said the shutdown and demolition of the Encina site would have to be part of any deal they’d approve.

“Our driving motive is to get the site as clean as possible,” Mayor Matt Hall said.

Carlsbad officials and many city residents have been against the proposed new plant since NRG filed its application with the California Energy Commission in 2007. At public hearings on the proposal in 2010 and 2011, hundreds of residents raised concerns about safety, air pollution and the destruction of coastal views.

Carlsbad unsuccessfully appealed the energy commission’s 2012 approval of the project, then took its case to the state Supreme Court, where the city lost again.

City officials said Tuesday they’ve spent more than $2.3 million fighting the plant.

Encina, whose 400-foot cooling tower looms over Interstate 5 on one side and the beach on the other, accounts for 7 percent of the generation capacity of a broad swath of San Diego and the Los Angeles Basin that once was served by San Onofre’s twin reactors.

Environmental deadlines for phasing out Encina’s so-called once-through cooling systems — a detriment to marine life — could render portions of the plant obsolete as soon as 2017.

Princeton, N.J.-based NRG won site approval last year for the Carlsbad Energy Center, which would involve retiring three of five existing Encina generators.

It’s unclear how much the Carlsbad plant might eventually cost. The Energy Commission estimated the capital costs would exceed $500 million.

Projects including the Carlsbad Energy Center are waiting on an official determination of the region’s long-term power needs by the California Public Utilities Commission. A decision may come as soon as the first quarter of 2014.

San Onofre stopped produced power on Jan. 31, 2012, when a small radiation leak uncovered rapid degradation of recently replaced heat exchange equipment.